The present invention generally relates to DC apparatus, and particularly to a DC apparatus suited to use as a power supply a DC voltage produced by restriction of AC components of source current.
Recently in the field of railroad vehicles, a system has become popular in which electric rolling stocks are driven by induction motors controlled by the output from a power converter that converts the DC voltage of overhead wire to an AC voltage of variable frequency/variable voltage.
In the railroad vehicles employing this type of system, the DC return current fed from overhead wire to the power converter is caused to flow to the rail along which the vehicle runs, and the rail is used as a railroad circuit through which a protective device installed on the ground can detect the presence of a vehicle. Therefore, if the return current to the power converter includes the same frequency component as the AC signal that flows in the railroad circuit, i.e., disturbance current, the railroad circuit could have erroneous operation. Thus, when the electric rolling stock running on the railroad is driven by the induction motor, it is necessary to remove the disturbance current included in the return current. Since the return current flowing in the railroad and the line current flowing in the filter reactor have the same value, the line current will hereafter be used unless otherwise noted.
The disturbance current included in the line current can be removed by the filter reactor, and filter condenser provided between the overhead wire and the power converter, but it is necessary to increase the inductance of the filter reactor and the capacitance of the filter condenser in order that the railroad circuit can be used at lower frequencies such as 25 Hz or 30 Hz as in the frequency division/multiplication railroad circuit. However, the increase of the capacitance and inductance of these elements will increase the weight, thus causing such problems as reduction of acceleration/deceleration performance, or increase of consumption power.
Thus, JP-A-57-145503 describes the system in which the disturbance current component included in the voltage across the filter condenser is detected and used to regulate the frequency of the induction motors, thereby reducing the disturbance current.
There is also proposed another system in which a resistor and a switching element connected in series are connected in parallel with the filter condenser, and a diode is connected in parallel with the resister so that the voltage across the filter condenser can be detected by a voltage detector. In addition, the output from the voltage detector is supplied to a function generator, which then produces 0 when the voltage Ecf of the filter condenser is less than a first reference voltage E1, 1 when the voltage Ecf of the filter condenser is equal to or larger than a second reference voltage E2, and a voltage proportional to the difference between the Ecf and the first reference voltage E1 when it is equal to or larger than E1 and less than E2. The output from the function generator is fed to a comparator, and a triangular wave with an amplitude of 0xcx9c1 generated from a triangular wave generator is also applied to the comparator so that the triangular wave and the output from the function generator can be compared by the comparator. If the output from the function generator is larger than the triangular wave, the switching element is made conductive. If the output from the function generator is less than the triangular wave, the switching element is made nonconductive. Thus, the switching element is controlled on and off according to the output from the comparator so that the current bypassing the power converter can be controlled.
According to this system, when the induction motor is decelerated, a torque opposite to the rotation direction is generated, so that the kinetic energy of the induction motor is converted to electric energy, and that the AC current fed to the power converter is converted to DC current. In other words, when the induction motor is regeneratively driven, the electric energy is regenerated on the overhead wire through the power converter. However, when the electric energy cannot be regenerated through the overhead wire to the DC power supply, the voltage Ecf of the filter condenser is increased. If the filter condenser voltage Ecf is excessively increased, the power converter and the filter condenser will sometimes break down.
Thus, in order to prevent this damage, the output of the function generator is set to be large, and the conduction period of the switching element is increased so that the current flowing in the resistor is controlled to increase. The increase of the current flowing in the resistor will result in much consumption of electric energy in the resistor, and hence the voltage Ecf of the filter condenser can be suppressed from rising. The diode acts to make the current due to the induction component of the resistor flow back when the switching element is made off.
It is an object of the invention to provide a DC apparatus capable of suppressing an AC component included in the amount of DC electricity supplied from a DC power supply, and a vehicle using the same.
According to the former of the conventional examples, the disturbance current can be attenuated, but since the line current is controlled by regulating the frequencies of induction motors, delay is caused in control between the frequency as the amount to be handled and the line current as the amount to be controlled. In addition, since the characteristic is changed depending on the operation condition of the induction motors, the disturbance current cannot be effectively suppressed, and the amount of the attenuation is limited.
In the latter of the conventional examples, when the voltage Ecf of the filter condenser is increased, and when the switching element makes switching operation, i.e., at the time of regenerative operation, the disturbance current included in the line current can be suppressed, but when the voltage Ecf of the filter condenser is decreased, or when the motors make powering operation, the switching element is turned off, and thus the disturbance current cannot be suppressed.
According to the invention, in order to solve these problems, there is provided a DC apparatus having an electric equipment that operates according to the amount of DC electricity supplied from a DC power supply, an electric-amount detector for detecting the amount of DC electricity from the DC power supply, an AC component detector for detecting an AC component superimposed on the detected output from the electric-amount detector, and a control system for controlling the current that bypasses the electric equipment on the basis of the detected output from the AC component detector.
Also, according to the invention, there is provided a DC apparatus having an electric equipment that operates according to the amount of DC electricity supplied from a DC power supply, an AC component detector for detecting an AC component superimposed on the amount of DC electricity from the DC power supply, and a control system for controlling the current that bypasses the electric equipment on the basis of the detected output from the AC component detector.
When each of the above DC apparatus is constructed, the following elements can be added.
(1) The control system has a switching element connected in parallel with the electric equipment in order to control a current that bypasses the electric equipment on the basis of a switching signal, and a switching controller that generates the switching signal on the basis of the detected output from the AC component detector, thereby controlling the switching operation of the switching element.
(2) The switching controller generates the switching signal on the basis of the detected output from the AC component detector so that the AC component superimposed on the amount of DC electricity supplied to the DC apparatus and an AC component superimposed on the current flowing in the switching element can be cancelled out.
(3) The switching controller generates the switching signal by which the switching element is made conductive at least once during each second when the amount of DC electricity from the DC power supply is equal to or lower than a first setting value and equal to or higher than a second setting value that is lower than the first setting value.
(4) The amount of DC electricity is a DC voltage.
(5) The DC apparatus further has a reactor connected in series with the DC power supply, and a condenser connected in parallel with the electric equipment, and the electric-amount detector detects the voltage across the condenser.
(6) The DC apparatus further has a reactor connected in series with the DC power supply, and a condenser connected in parallel with the electric equipment, and the AC component detector detects the voltage across the reactor.
(7) The electric equipment is a power converter for converting a DC voltage to an AC voltage.
(8) Electric motors are connected to the AC output side of the power converter.
In addition, according to the invention, there is provided a vehicle having the DC apparatus as the power converter, wherein the wheels are driven by the induction motors connected to the power converter.
According to the above DC apparatus, the AC component superimposed on the detected output from the electric-amount detector or the AC component superimposed on the amount of DC electricity from the DC power supply is detected, and the current that bypasses the electric equipment can be controlled on the detected output. Thus, the AC component superimposed on the amount of DC electricity supplied from the DC power supply can be suppressed.
In other words, the current for canceling out the AC component of the disturbance current flowing in the electric equipment that is the source of the disturbance current is caused to flow in the control system as a current that bypasses the electric equipment, thereby making it possible to suppress the disturbance current that is the AC component included in the amount of DC electricity.
Thus, according to the invention, as described above, the AC component superimposed on the amount of DC electricity supplied from the DC power supply can be suppressed without increasing the size of the filter reactor and filter condenser.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.